1. Field of the Invention
The present invention relates to a protection device in a color display tube(CDT), and more particularly, to a device for preventing generation of X-ray and overvoltage, in which an over voltage or a heater voltage caused by an abnormal operation of a monitor applied to a CDT, or an over voltage from a power source applied to peripheral circuit is detected and cut-off, for preventing generation of an X-ray and over voltage.
2. Background of the Related Art
Being one of cathode ray tube, though the CDT provides high resolution and luminance by accelerating thermion by means of a high voltage and exciting a fluorescent film, in general, the CDT generates much X-ray which is harmful to human body. The FDA(Food and Drug Administration) regulates a radiation exposure rate caused by a TV receiver such that the rate should not exceed 0.5 milliroentgen per hour at any point 5 cm away from an external surface of the receiver. Accordingly, a device for preventing generation of an X-ray is employed in the monitor circuit for satisfying the FDA regulation.
FIG. 1 illustrates a block diagram showing a related art device for preventing generation of an X-ray in a CDT.
Referring to FIG. 1, the related art device for preventing generation of an X-ray in a CDT is provided with a power supply part 1 for converting an AC voltage to a DC voltage and supplying different voltages B.sup.+ and B.sup.2+ required by different parts, a flyback transformer 2 for boosting a supply voltage B.sup.2+ from the power supply part 1 according to a horizontal deflection pulse from a horizontal deflection outputting part 5 to provide a voltage required for a regular operation of a CDT 3 as well as a heater voltage H/V to an anode, a CDT 3 for emitting electron beams inclusive of an X-ray by means of the heater voltage H/V from the flyback transformer 2, an X-ray detecting part 4 for detecting an X-ray emitted from the CDT 3 and applying to the horizontal deflection outputting part 5, and the horizontal deflection outputting part 5 operative on the supply voltage B.sup.+ from the power supply part 1 for providing different horizontal deflection pulses according to an intensity of the X-ray from the X-ray detecting part 4 for controlling operation of the flyback transformer 3. In the aforementioned related art device for preventing generation of an X-ray, the high voltages required for operating the CDT 3 are fixed according to sizes of the CDTs and manufacturer's specifications. If the high voltage is within a limitation, a safety of the CDT 3 is secured and the X-ray radiation therefrom gives no harm to a human body, if the high voltage exceeds the limitation, not only the safety of the CDT 3 can not be assured, but also the X-ray radiation may give a fatal harm to the human body because the X-ray radiation increases proportional to the intensity of the high voltage. In order to prevent this, when the power supply part 1 converts an AC voltage into a DC voltage and supplies driving voltages for driving different peripheral circuits, the horizontal deflection outputting part 5 provides different deflection pulses according to the driving voltage B+ from the power supply part 1 and the intensity of the X-ray from the X-ray detecting part 4 to control the flyback transformer 2, thereby preventing radiation of X-rays around the CDT 3. According to this, the flyback transformer 2 boosts the supply voltage B.sup.2+ from the power supply part 1 according to an wound ratio to supply different stable voltages, such as the high voltage, a luminous voltage, a focus regulating voltage, and a heater voltage L/V to the CDT 3. In this instance, the X-ray detecting part 4 detects an X-ray from the high voltage H/V applied from the flyback transformer 2 to the anode terminal on the CDT 3. That is, the X-ray detecting part 4 detects a change of the high voltage H/V applied to the CDT 3 which rises in proportion to a rise of a high voltage caused by characteristics changes of circuit components, and, if the voltage change is higher than a value preset for each product(or the high voltage is higher than a preset value), the voltage change is applied to the horizontal deflection outputting part 5. The horizontal deflection outputting part 5 then compares the X-ray signal from the X-ray detecting part 4 to a reference signal, to cut off generation of the horizontal deflection pulses when the X-ray signal exceeds the reference signal. In this instance, since the flyback transformer having no horizontal deflection pulse applied thereto is not operative, the CDT 3 is not operative, too. Thus, the related art device for preventing generation of an X-ray protects the CDT 3 and cuts off the radiation of the X-ray by detecting a rise of the high voltage H/V caused by an abnormal high voltage applied to the CDT 3 and regulating generation of the horizontal deflection pulse.
However, the related art device for preventing generation of an X-ray has a problem of much power consumption because entire peripheral circuits inclusive of the power supply part except the flyback transformer and the X-ray detecting part are operative regularly even if operation of the CDT is stopped by cutting off generation of the horizontal deflection pulses at detection of the X-ray caused by a rise of the heater voltage from the flyback transformer.